The couplings without stops are called repair couplings.

When running copper it is best to use standard couplings with stops to insure the pipe is inserted deep enough into the coupling to make a good joint, however sometimes when making a repair in close quarters you can't move the pipe enough to get a coupling in so they make the repair couplings that can be slid on one pipe, the pipes lined up, then slide the coupling over the joint.

A good trick when using repair couplings is to align the two pipes and hold the coupling beside the pipe to insure it is centered over the joint, then make a mark on the pipe with a felt tip. You can then slide the coupling on one pipe, apply your flux and slide the coupling over the joint till it is aligned with the felt tip mark. That way you will be sure the actual joint is centered in the coupling.

Thanks for the repair coupling tip and info.